The invention relates to an air spring which has a flexible member which, on the one hand, is attached to a housing and, on the other hand, to a roll-off piston and encloses an air volume. The surface of the housing, which faces toward the air volume of the air spring, is charged with the air pressure of the air volume and this surface of the housing can be connected to the chassis of the motor vehicle at the housing end with an elastic bearing disposed therebetween.
From the state of the art, air spring struts are known (see, for example, U.S Pat. No. 4,712,776) which comprise a shock absorber and an air spring. The air spring is supported at the end of the roll-off piston on the cylinder of the shock absorber. The piston of the shock absorber is insertable into the cylinder and is connected to the housing via an elastic bearing for wobble movement and this permits a pivot movement of the shock absorber relative to the air spring. A further elastic bearing is mounted above the housing of the air spring via which the total air spring strut is connected to the chassis of a motor vehicle. The additional bearing makes possible a pivot movement of the entire air spring strut in its upper region. Because of the pivot movements, transverse forces and thrust stresses, which act on the flexible member of the air spring with the deflections of the air spring, can be reduced and this leads to a longer service life of the flexible member. It is, however, noted that the total force flow of the wheel load passes through the elastic bearing mounted above the housing of the air spring. This must be configured correspondingly large and hard in order to withstand the loading generated by the wheel load. The bearing therefore requires considerable space, which is dimensioned sparingly. Furthermore, the hard configuration of the bearing leads to limits on comfort of the motor vehicle because the air spring of the spring strut as well as the elastic bearing, which is mounted above the housing of the air spring, exhibits a high spring stiffness when there are small vibration amplitudes of the air spring strut. Vibrations having a small vibration amplitudes are therefore poorly cushioned.
It is an object of the invention to provide an air spring which is suitable for installation in an air spring strut and which air spring has an elastic bearing in the upper region for wobble movement which bearing connects the air spring to the chassis of the motor vehicle and requires little space.
The above object of the invention is realized in that: the housing of the air spring comprises at least two parts of which a first part functions to connect the air spring to the chassis of a motor vehicle and a second part functions to attach the flexible member; and, that the elastic bearing is configured so as to be annular and is mounted between the two parts of the housing.
The elastic bearing connects the two parts of the housing air-tight to each other so that no air from the air volume of the air spring can escape to the outside between the two housing parts. The surface of the first part of the housing, which faces toward the air volume of the air spring, is charged with the air pressure of the air volume of the air spring. The surface of the first part of the housing, which is pressure-effective in the longitudinal direction of the air spring, corresponds in its size preferably approximately to the pressure-effective area of the air spring or is larger. In this way, it is ensured that the total wheel force is compensated by the force which the air pressure in the air volume of the air spring applies to the pressure-effective surface of the first part of the housing which is directed in the longitudinal direction of the air spring. The static wheel load does not operate on the elastic bearing.
The advantage achieved with the invention is especially that the force flow of the wheel load leads directly from the air volume of the air spring to the chassis and, in this way, the elastic bearing of the air spring is no longer loaded completely by the wheel load. For this reason, the elastic bearing can be configured to be small and requires little space. A further advantage of the invention is that the elastic bearing can be configured to be softer because of the lower loading by the wheel load and, in this way, especially vibrations having a small amplitude and a high vibration frequency can be cushioned by the bearing. Thus, the spring characteristic of the air spring is improved for the above-mentioned vibrations.
According to a feature of the invention, the clear diameter of the elastic bearing corresponds approximately to the effective diameter of the air spring. The advantage of this further embodiment is that the elastic bearing is neither subjected to compression nor tension by the air pressure in the air volume of the air spring and is subjected to only a minimum load. In this way, it is possible to configure the elastic bearing to be especially small and especially soft.
According to another feature of the invention, the roll-off piston of the air spring supports itself on a cylinder of a shock absorber whose piston is connected to the second part of the housing and is insertable into the cylinder. Because of the elastic bearing between the first part and the second part of the housing of the air spring, it is ensured that the shock absorber is wobble movable relative to the housing of the air spring in the upper region thereof. For this reason, an elastic bearing is not needed in the region of the attachment of the insertable piston at the second part of the housing.
According to a further feature of the invention, the roll-off piston supports itself on a cylinder of a shock absorber whose piston, which is insertable into the cylinder, is connected directly to the chassis so as to be wobble-movable. The wobble-movable connection of the piston to the chassis takes place preferably via an elastic bearing. The advantage of this embodiment is that the force flow of the dynamic forces is directed directly from the shock absorber to the chassis of the motor vehicle. These dynamic forces operate on the shock absorber with a spring operation of the air spring strut. The force flow does not pass through the elastic bearing, which lies between the two parts of the housing of the air spring, so that these dynamic forces do not have to be considered when designing the elastic bearing. In this way, the space needed to accommodate the elastic bearing can be minimized. Furthermore, the elastic bearing (via which the insertable piston of the shock absorber is connected to the chassis of the motor vehicle) is optimally matched to the dynamic forces acting on the shock absorber.
According to a further feature of the invention, the elastic bearing has a form approximately of an annular section of a spherical surface and is mounted between two flange-like collars of the first and second parts of the housing. The pivot point of the spring in its upper region is then given by the center point of the spherical surface, which is completed starting from the annularly-shaped bearing. The advantage of this embodiment is that the pivot point of the air spring can be precisely fixed in the upper region because of the suggested configuration of the elastic bearing.
According to another feature of the invention, the elastic bearing is in the form of an annular cutout of a spherical surface and is mounted in such a manner between the two parts of the housing that the center point of the spherical surface, which is completed starting from the annularly-shaped bearing, and therefore the pivot point of the air spring strut, lies in the region at which the piston of the shock absorber is connected to the chassis. The advantage of this embodiment is that the spring strut can pivot about this point free of stresses.
According to still another feature of the invention, the elastic bearing comprises an elastomer component. The advantage of this embodiment is that the elastic bearing in the form of an elastomer component can be configured especially simply. Furthermore, an elastic bearing in the form of an elastomer component is especially suitable to place the two parts of the housing air-tight against each other.
A further feature of the invention is characterized in that: the flexible member projects beyond the second part at that end with which it is attached to the second part of the housing; and, that the part of the flexible member, which projects beyond the second part, is attached in such a manner to the first part, that a yielding part of the flexible member remains between the first and second part of the housing and the yielding part defines the elastic bearing.
The advantage of this embodiment is that for the elastic bearing, no separate component need be made available. A further advantage of this embodiment is that the flexible member can be attached to the parts of the housing simply with the aid of clamping rings and this attachment ensures an air-tight connection of the two parts of the housing.